Embodiments of the inventive concepts relate to an image sensor, and more particularly, to an image sensor including a pixel circuit array that operates using a global shutter without a mechanical shutter.
A complementary metal oxide semiconductor (CMOS) image sensor is a device that is installed in a portable phone camera, a digital still camera and so on to convert a scene unfolded to the sight into a screen image through a display device.
In detail, the CMOS image sensor converts a scene into an electrical signal using a photoelectric element, converts the electrical signal into a digital image signal, and sends the digital image signal to a display device such as a liquid crystal display (LCD). The digital image signal output from the CMOS image sensor is image data of red (R), green (G) and Blue (B).
The photoelectric element is a device that generates photocharge in proportion to the quantity of incident light. A photodiode is an example of the photoelectric element. When very strong light is applied to the photodiode, photocharges above a capacity that the photodiode can store therein may be generated. As a result, the photocharges may overflow the photodiode and the excess overflow charges may affect adjacent pixels resulting in a distorted image.
The distorted image may be a white image or an indiscernible image. Such a phenomenon that brings aberration into an output image is called a blooming phenomenon.
In order to prevent the blooming phenomenon that occurs due to very strong light, a mechanical shutter is used to adjust the quantity of light applied to the photoelectric element.
However, when the mechanical shutter is used manufacturing cost and the size of an image device increase and an operating cycle is limited. Accordingly, the mechanical shutter is used in high-grade cameras and is generally not used in low-price compact cameras.
For low-price or compact cameras in which the mechanical shutter is not used, a pixel circuit having a global shutter function performing a global shutter operation has been developed. In the global shutter operation, all photoelectric elements in a frame simultaneously receive light, all signals from the photoelectric elements are transferred to a floating diffusion layer at a time, and then image signals corresponding to a row, which is sequentially selected, are output.